Well-known playback controls that can be used in commercially produced playback apparatuses include fast-forward, fast-rewind, chapter skip, pause (temporary suspension), angle change, audio change, and menu call. Playback controls are expected to increasingly diversify as new package media in a new data format such as DVD-Videos and BD-ROMs appear on the market.
Whether a specific playback control is enabled or disabled depends on where the current playback point in a playback timeline of the digital stream. In order to perform a playback control such as “angle change”, multiple pieces of video data recorded in a specific data structure must be present. In other words, the angle change cannot be executed unless the current playback point reaches a point at which such a specific data structure exists. The angle change becomes available only when the current playback point reaches the point at which the specific structure exists.
Conventionally, however, there has been no way of informing a user that such a point has been reached, which means the user often misses the chance to instruct the playback apparatus to perform a playback control, or waste time for trying to instruct the playback apparatus to perform a disabled playback control without realizing that a playback control is unavailable.
One solution to inform the user of the availability of playback controls at the current playback point is to display navigators in a display screen. Navigators are GUIs that aid the user's thinking and decision making by displaying available operations and parameters, and are often seen in video games and such. The problem of the user missing the chance for the playback controls is thought to be avoided by displaying navigators on the screen to inform the user of the enabled playback controls at the current playback point. However, the display of navigators has caused persistent objections from producers who engage in movie production. Movie producers create each scene of a movie work based on their own artistic sensitivity. Producers take offense if navigators are merged in scenes of their movie works, because this represents a kind of alteration to the movie work.